Friday, October 19, 2012

USING ALFALFA AND GRASS HAYFIELDS AFTER FROST

Some Thoughts and Considerations

Rory Lewandowski, Extension Educator Wayne County and Crossroads EERA

We have had some frost over the past
week and one question that comes up is the use of alfalfa and/or grass
hayfields following a frost.Management
after a frost depends upon several factors. Was there a frost or a killing freeze? Is the
hayfield a legume or a grass stand? What are the needs and goals of the
hayfield’s owner.

Temperature is a consideration.A frost may burn the top of the plant, but
growth will still continue from the green, unburned leaf area.A killing freeze for alfalfa is generally
defined as a temperature in the 24 to 25 degree F range over a period of at
least 4 hours.After a killing freeze,
alfalfa is done growing and the plant can be cut for mechanical harvest,
grazed, or left to overwinter.

This
year, because of the drought, livestock producers need all the forage they can
get so many livestock owners are cutting hay fields regardless of the calendar
or weather forecast. Alfalfa is the
forage we generally hear a lot about regarding fall management.One reason for that is because alfalfa
regrows by mobilizing and using carbohydrate root reserves to produce new leaf
growth after a cutting.At some point,
there is enough new leaf area that sugars manufactured by photosynthesis meet
the plants growth needs plus have surplus to put back into root reserves. If management during the growing season has
left low levels of root reserves and now the plant is cut in the late fall,
burns more reserves to start growth, but the growing season ends before the plant can
grow enough leaves to restore those root reserves, then there is risk of the
plant dying over the winter.The reason
the recommendation is made to not cut alfalfa between about mid-September until
a killing frost is to protect those plant root reserves.

So, does this mean that all the alfalfa we have seen around the state that has been cut before a killing frost is going to die over the winter? No, while some stands will be hurt by this management, other stands will not, or only be impacted in a minimal way. That is because there are other factors that play a role in determining winter kill. Factors
that affect winter kill include cutting date in the fall which I have mentioned, but there is less winter kill risk when a fall cutting is taken on a
young vs. an old alfalfa stand, and less risk when the stand is planted on a
well-drained site.In addition soil fertility is important. Stands that have maintained good soil fertility, especially soil potassium levels and that have kept
soil pH close to that 6.8 level have reduced risk of winter kill. Finally growers who use improved
genetic varieties with good disease resistance and over wintering levels have reduced risk.

Sometimes
the question is asked if too much top growth can lead to smothering over the
winter.In alfalfa this is not an issue
because the leaves will dry up following a killing freeze, become brittle and
drop off the plant.The stem that
remains standing is not a concern for smothering the stand.Tall grass plants however can mat down.This mat can provide a habitat favorable for
disease development that could thin out the stand.For this reason, it is recommended that a
grass hay field with tall growth be cut or grazed before winter.

With our shorter days and cooler
temperatures it becomes very difficult to get a cut legume or grass to dry down
enough to bale as a dry forage.Wrapping
wilted forage or harvesting as baleage is the best mechanical option.Grazing a hayfield is usually a more economical
option as compared to mechanical harvest.Use of temporary electric fencing can facilitate the grazing use of a
hayfield.While forages such as alfalfa,
clovers and cool-season perennial grasses do not produce toxic compounds after
a frost, bloat can be a concern when alfalfa or clovers are grazed after a
frost.

The risk of bloat is higher one to
two days after a killing frost and when livestock are grazing a pure or mostly
pure legume stand.The safest management
practice is to wait a few days after a killing frost before grazing pure legume
stands.At that point the forage will
begin to dry from the frost damage. If
animals are not accustomed to grazing high legume content stands, it is a good
idea to feed some dry hay before turning into the legume field, or move animals
into the legume field in the late morning or early afternoon after they have
been grazing another pasture so that they are not entering with an empty rumen.

Subscribe To

Ohio State University Extension embraces human diversity and is committed to ensuring that all research and related educational programs are available to clientele on a nondiscriminatory basis without regard to race, color, religion, sex, age, national origin, sexual orientation, gender identity or expression, disability, or veteran status. This statement is in accordance with United States Civil Rights Laws and the USDA. Keith L. Smith, Ph.D., Associate Vice President for Agricultural Administration and Director, Ohio State University ExtensionTDD No. 800-589-8292 (Ohio only) or 614-292-1868